OR validation for React props

component.js

const Component = React.createClass({
  propTypes: {
    file: requireThisOr('files', React.PropTypes.instanceOf(File).isRequired),
    files: requireThisOr('file', React.PropTypes.arrayOf(React.PropTypes.instanceOf(File)).isRequired)
  }
})

validator.js

export default function requireThisOr(otherProp, propValidator) {
  return (props, propName, componentName) => {
    if (!props[otherProp]) {
      return propValidator(props, propName, componentName);
    }
  };
}